Segregation of Niobium During Electroslag Remelting Process

Experiment was carried out after the process parameters were calculated by the model previously established. The relationship between interdendritic spacing and local solidification time （LST） mainly determined by process parameters was exposed. Furthermore, the extent of segregation was studied. The results indicate that LST and interdendritic spacing are the largest and the amount of Laves phase as a result of the niobium segregation is the highest in the center of the ingot, whereas the opposite results are obtained at the edge of ingot. The extent of element segregation and the amount of Laves phase can be reduced when appropriate parameters are used. Therefore, the duration of subsequent homogenization treatments for 718 is shortened and the alloy quality is improved.

Metallurgical Source of Cryogenic Intergranular Fracture of Fe-38Mn Austenitic Alloy

SEM and Field emitting TEM-EDAX were used to investigate the fracture surface of series impact specimens and the grain boundary chemistries of VIM(vacuum-inductionmelted) Fe-38 Mn austenitic alloy before and after ESR(electroslag remelting,).The quantity and the size of inclusions were also examined.The results show that the VIM Fe-38 Mn austenitinic alloy water-quenched from 1 100 C undergoes an obvious ductile-to-brittle transition,and the impact work at ambient temperature is 242 J,the corresponding fracture surface exhibits a dimple character.However,the impact work at 77 K of VIM alloy is only 25 J and the fracture mode is IGF(intergranular fracture).After ESR,the impact work at ambient temperature is 320 J and the fracture surface exhibits a character of "volcano lava"(meaning excellent toughness);The impact work at 77 K is up to 300 J and the fracture mode is micro void coalescence mixed with quasi-cleavage.The segregation of Mn is not found in all specimens,but the segregation of S is observed,and the S segregation is decreased after ESR.The examined results of inclusions show that ESR reduces the quantity and improves the morphology of inclusions.From the above results it can be seen that the cryogenic IGF of VIM Fe-38 Mn austenitic alloy is related to the S segregation at grain boundary.After ESR the decrease in the quantity and size of inclusion results in the increase of the impact work at ambient temperature,while the restriction of IGF is related to the decrease in the total level,and hence in the grain boundary segregation of S.

电渣熔铸35CrNi3MoV钢枝晶间断裂的俄歇分析

用扫描俄歇探针和金相法研究了电渣熔铸３５ＣｒＮｉ３ＭｏＶ钢断口上亮线、亮点的本质和形成机理。结果表明，它们是铪、氮、硫在枝晶间偏聚并形成ＨｆＮ从而脆化了枝晶间区域的结果。当裂纹沿着枝晶间的贝氏体条带扩展时就形成亮线，当裂纹斜穿贝氏体条带时就形成亮点。亮线（亮点）显著降低钢的力学性能，提高渣料纯度是避免电渣铸钢产生这种缺陷的关键措施。